A conventional transmission mounted on a vehicle is provided with a machine room arranged in a casing and accommodating a plurality of gears including a differential gear, a control room positioned adjacent to the machine room in the casing and accommodating a mechanism for hydraulic pressure control of a hydraulic pressure control body, and an oil sump section arranged in an interspace between an inside surface of the casing and the differential gear in the machine room. Such transmission includes a lubricating oil supply structure for supplying oil in the casing to places in need of lubrication such as bearings supporting a rotation shaft and the gears. As described for example in Patent Documents 1, 2, some of such lubricating oil supply structures use oil scooped up by the differential gear. In the transmission, this lubricating oil supply structure forms oil films on and cools tooth surfaces of the gears, an inside of the rotation shaft and shaft supports including the bearings, thereby securing smooth performance and intensity durability of each component in the casing.
However, the lubrication structure using oil scooped up by the conventional differential gear has following problems (A1)-(A4).
(A1) Oil scooped up in the machine room (a differential room) by the differential gear drop again in the machine room along an inner wall surface of the casing, whereby enough oil does not return to the control room and an oil surface thereof is lowered. Due to this, an oil inlet provided on a bottom of the control room or in a vicinity thereof is exposed from the oil surface, allowing air biting (aeration) to occur.
(A2) On the bottom of the machine room, a communicating passage (an oil inflow part) is formed, communicating to the bottom of the control room. Part of oil in the control room is adapted to return to the machine room via this communicating passage. And, this communicating passage is formed in an interspace between the inside surface of the casing and a partition wall integrally formed to the casing. Namely, this communicating passage is a part formed by processing the casing. Therefore, stress (intensity) necessary for the casing disallows dimensions of the communicating passage to be too small, thereby failing to appropriately control a flow rate of the oil flowing into the machine room from the control room. Accordingly, an oil amount in the machine room increases, resulting in increased scooping-up resistance against the differential gear.
(A3) An oil sump section which is a space where oil is collected is formed in an interspace between a side surface of the differential gear in the machine room and an inside surface of the casing facing thereto. However, as the side surface of the differential gear is contacted with (dipped in) the oil collected in this oil sump section, the oil in the oil sump section is stirred when the differential gear rotates, causing to an increase in oil stirring resistance.
(A4) On the inside surface of the casing facing to the side surface of the differential gear, as shown in Patent Document 3 for example, a lubricating oil passage for leading part of oil scooped up in the machine room to shaft supports such as bearings of the differential gear and a spline engagement section is formed. However, as this lubricating oil passage is a ditch-shaped (hollow-shaped) section formed on the inside surface of the casing, most of the lubricating oil passing through this lubricating oil passage drop out thereof on the way into the machine room. Therefore, there is the problem that this lubricating oil passage cannot supply an enough amount of lubricating oil to the shaft supports of the differential gear.
It should be noted that some structures regulating a hydraulic fluid flow in the casing of the transmission are provided with a baffle plate installed in the casing as shown in Patent Documents 4 and 5. Such baffle plate can regulate the hydraulic fluid flow in the casing to a desired state and prevent the hydraulic fluid collected at the bottom in the machine room from being stirred due to rotation of the differential gear. However, any conventionally-structured baffle plate, any single baffle plate in particular, which can solve all the above-mentioned problems: (A1)-(A4) has not been available.